90 ELPTO 2 Stroke Hesitating, dying at high rpm

[gydatree]

I recently installed a replacement powerhead on this outboard. It had blown the bottom piston in the old one with a bad voltage regulator. It cranks right up no problem, idles a tad rough just under 1000 rpm in the water. Once you get going at low rpms it seems to vibrate the aluminum siding on the pontoon a bit. Upon acceleration to about 3000 rpms it hesitates, but will cruise for a bit at least.

Once you try to open it to about 4500-5500 rpms it hesitates for a few seconds, but will kick in and get up to about 5000 rpms running great pushing the boat fine, but will start to die down and eventually stall out unless you pull it back to idle in time and sometimes pumping the bulb on the fuel line will keep it going, and if it stalls you have to re prime the fuel line which does hold pressure until you start opening the throttle.

There are no visible fuel leaks anywhere, and i blew out all the lines with pressured air, but now that i think about it im not sure if i pressure tested all of them. The carbs and fuel pump are freshly rebuilt with new gaskets etc.

I am thinking my next step is to pressure test the fuel lines and maybe replace the fuel pump diaphram. I tried a different bulb in the line from another boat and didnt see any difference.

So do you guys think Im close or could there could be an issue maybe with the enrichment valve or timing or ignition system that I am not linking the issue too?

 

[Silvertip]

Until you repair the fuel pump you will be chasing your tail. The fact that pumping the primer bulb causes it to run correctly says the fuel pump is not capable of supplying the needed fuel at high rpm. It will only get worse with time so do it now. Also make sure the vacuum source to the pump does not have a leak. A leak at the vacuum port means the pump can't work correctly.;

 

[Texasmark]

Besides what Silvertip said that I support, what did you have with the old powerhead before you blew it? If everything was ok then we can eliminate things like right prop and right engine for the boat and correct setup and all that.

First of all I had one of those and they weren't smooth at low rpms, especially with a high pitched (13+x24 Ballistic XL SS) I liked to run at 5700ish rpm.
Second the link and sync (synchronization) sets the timing After TDC by a few degrees at the book idle rpm (in the water, boat moving in F gear, at 675 +/- 50 rpm), to 20 -22 depending on how you set the timing....manual specifies which applies to which arrangement at WOT. If the timing is lagging due to incorrect setting, it can definitely influence your performance.

Then there's the carb part of the link and sync . Manual tells you how to set that up too and notes that the idle speed is set by varying the timing (with the idle speed nylon knurled set screw on the linkage arm), not the carburetor fuel flow. Then there is more in the link and sync in setting the low speed jets at around 1.5 (check manual) and then adjust for best plane out on the water.....meaning idling in F gear, firewalling the throttle, engine grunts and takes the load with a good solid response and quick plane out....several seconds. If not achieved, opening of the jets till accomplished....a tad at a time on all 3.

Then there is the possibility of carbs needing a cleaning anyway, replacement of fuel lines due to deterioration from today's fuels which includes the fuel line from the tank to the engine and bulb. I had tan scale develop in my tank to engine fuel line after 10 years of age that got so bad it clogged up the line at the bulb.

Then there are the stat and bypass (popoff) valves on this replacement powerhead to question...stat particularly at rpms below 2500 (manual stated number) and the popoff above.